Conventionally, as a method of forming a thin film on a dielectric, silicon, or other substrate, for example, there is a thin film forming method by making a material of the thin film (hereafter, this is called a thin film material) into particulates, and making the particulate thin film material on the substrate. As the thin film forming methods, depending on difference between methods of making the thin film material into particulates, methods of making it deposited, and the like, for example, there are a sputtering method, a CVD (Chemical Vapor Deposition) method, an MBE (Molecular Beam Epitaxy) method, a laser ablation method, a vacuum deposition method, etc.
In addition, generally, thin film forming systems which are used when forming a thin film using the sputtering method etc. are classified into systems called a parallel plate type and an opposed type according to positional relation between a substrate, on which the thin film is formed, and a target for generating the particulate thin film material.
The parallel plate type thin film forming apparatus is arranged, for example, as shown in FIG. 13, so that a first principal surface 1A of the substrate 1, and the target 2B may be in parallel. At this time, the target 2B is mounted on a cathode 3, and by supplying electric power to the cathode 3, the particulate thin film material 2A is sputtered out of the target 2B between the target 2B and the substrate 1. Then, for example, by applying an electric field between the target 2B and the substrate 1, introducing the particulate thin film material 2A in a direction of the substrate 1 with accelerating it, and depositing the particulate thin film material 2A on the first principal surface 1A of the substrate 1, the thin film 2 is formed. In addition, at this time, the substrate 1 is fixed to a heat stage 13, and is heated from a backside 1B of the first principal surface 1A of the substrate 1 (hereafter, this is called a second principal surface) as shown in FIG. 13.
In the case of the parallel plate type thin film forming apparatus, the particulate thin film material 2A which is accelerated and is in a high energy state collides at a nearly vertical angle to the thin film formation surface of the substrate. Therefore, while the film formation speed of the thin film 2 is fast and productive efficiency is high, there is a problem that a damage to the surface of the thin film 2 deposited on the substrate 1 is serious. In order to make the damage to the surface of the thin film 2 small, for example, there is a method of making an acceleration of the particulate thin film material 2A small. Nevertheless, when an acceleration of the particulate thin film material 2A is made small, film formation speed of the thin film 2 drops, and productive efficiency drops. Then, in recent years, for example, the opposed type thin film forming apparatus is proposed as a thin film forming apparatus which replaces the parallel plate type thin film forming apparatus.
The opposed type thin film forming apparatus is arranged, for example, as shown in FIG. 14, so that two targets 2B may face each other on an extension in a direction parallel to an in-plane direction of the first principal surface 1A of the substrate 1. Also at this time, the each target 2B is mounted on a cathode 3, and by supplying electric power to the cathode 3, the particulate thin film material 2A is sputtered out of the targets 2B. Since the particulate thin film material 2A which is sputtered out of the each target 2B gather between the two targets 2B facing each other, when the particulate thin film material 2A is accelerated by applying an electric field between the two targets 2B, and are introduced on the first principal surface 1A of the substrate 1, the thin film material 2 is formed by the particulate thin film material 2A being deposited on the first principal surface 1A of the substrate 1.
In the case of the opposed type thin film forming apparatus, since an incident angle at the time of the particulate thin film material 2A colliding with the first principal surface 1A of the substrate 1 is as small as about 0° to 45°, damage which the thin film 2 deposited on the first principal surface 1A of the substrate 1 receives is small when the particulate thin film material 2A collides with the first principal surface 1A of the substrate 1. Therefore, since it is possible to introduce and deposit the particulate thin film material 2A on to the first principal surface 1A of the substrate 1 in a high energy state, and it is possible to form the thin film 2 damage of whose surface is small without reducing productive efficiency.
In addition, since other methods such as the CVD method, MBE method, laser ablation method, and other film formation methods also form a thin film with principles and apparatuses similar to the sputtering method, detailed description is omitted.
The parallel plate type and opposed type thin film forming systems are used, for example, when producing microwave devices such as a GPS (Global Positioning Systems) array antenna and a microwave integrated circuit. In the microwave device, for example, as shown in FIGS. 15 and 16, a circuit pattern 2C is provided on the first principal surface 1A of the substrate 1, and a ground plane 2D is provided on the second principal surface 1B of the substrate 1. Here, FIG. 16 is a sectional view taken on line D-D′ in FIG. 15.
The microwave device is operated using a change of a magnetic field generated in connection with a leakage electric field generated between the circuit pattern 2C and the ground plane 2D, for example, as shown in FIG. 17. At this time, when the circuit pattern 2C and the ground plane 2D are oxide layer superconductors, for example, it is possible to obtain smaller surface resistance and higher operating characteristics in comparison with usual conductors. Therefore, recently, various microwave devices using the oxide superconductors have attracted attention (for example, refer to S. 0hshima, “High-temperature superconducting passive microwave devices, filters, and antennas”, Supercond. Sci. Technol., 13, 2000, p. 103-108).
In a microwave device using the oxide superconductors, for example, a dielectric substrate such as magnesium oxide (MgO) or sapphire (A1203) is used for the substrate 1, and oxide superconductors such as YBCO or BSCCO are used for the circuit pattern 2C and the ground plane 2D.
When producing a microwave device using the oxide superconductors, first, as shown in FIG. 18, thin films 2C′ and 2D of the oxide superconductors are formed on the first principal surface 1A and the second principal surface 1B of the dielectric substrate 1, respectively. The parallel plate type and opposed type thin film forming apparatuses are used for formation of the thin films 2C′ and 2D. At this time, it is assumed that the target 2B is constructed of, for example, a material of YBa2CU3Ox, Y203, BaO, CuO, or the like which is used for formation of YBCO which is one kind of oxide superconductors. In addition, the dielectric substrate 1 is heated at, for example, about 800° C. at this time.
In addition, when forming the thin films 2C′ and 2D, for example, after forming the thin film 2C′ on the first principal surface 1A of the dielectric substrate 1, the dielectric substrate 1 is turned over, and the thin film 2D on the second principal surface 1B of the dielectric substrate 1 is formed. At this time, respective thin films 2C′ and 2D on the first principal surface 1A and second principal surface 1B of the dielectric substrate 1 are formed with composition of target 2B and conditions in an apparatus at the time of formation being fixed, for example, so as to become the same film quality and film thickness.
Next, as shown in FIG. 19, an etching resist 12 matched with the circuit pattern 2C is formed on one thin film, for example, the thin film 2C′ on the first principal surface 1A of the dielectric substrate 1. At this time, although illustration is omitted, a resist is formed, for example, also on the backside of the surface on which the etching resist 12 is formed, that is, the thin film 2D on the second principal surface 1B of the substrate 1. Then, unnecessary portions are removed by etching the thin film 2C′ on the surface on which the etching resist 12 is formed, and the circuit pattern 2C as shown in FIG. 15 is formed.
Nevertheless, when forming the thin films 2 in both sides of the substrate 1 by the conventional art, it is necessary to form single sides separately. Therefore, for example, while turning the substrate 1 over and forming the thin film 2 on the second principal surface 1B of the substrate 1 after forming the thin film 2 on the first principal surface 1A of the substrate 1, film quality of the thin film 2 formed on the first principal surface 1A of the substrate 1 may change. In particular, when forming the thin films 2C′ and 2D of the oxide superconductors like the microwave device, there was a problem that degradation of the film quality due to a timing change occurred easily.
In addition, even if thin films are formed under the same conditions using the same thin film forming apparatus, it is apt to generate difference between the film qualities of the thin film 2 formed at a time and the thin film 2 formed at a second time because of states of the target 2B, temperature unevenness at the time of heating, etc. Therefore, the conventional methods for forming a thin film had a problem that it was difficult to equalize the film qualities of the thin film of the first principal surface 1A and the thin film of the second principal surface 1B of the substrate 1.
In particular, the oxide superconductor used when producing the device is deficient in chemical stability. Therefore, when forming single sides separately at the time of forming the thin films 2C′ and 2D of the oxide superconductor on both sides of the substrate 1, degradation of the film quality and decrease of uniformity of the thin film 2C′ formed on the first principal surface 1A and the thin film 2D formed on the second principal surface 1B of the dielectric substrate 1 are apt to be generated. Therefore, for example, there was a problem that difference between electrical characteristics of the circuit pattern 2C, and electrical characteristics of the ground plane 2D arose and operation of the device became unstable.
In addition, upsizing of the substrate 1 used for manufacturing the microwave device etc. has been advancing recently. Therefore, when forming single sides separately at the time of forming thin films on both sides of the first principal surface 1A and the second principal surface 1B of the substrate 1, degradation and unevenness of film quality become remarkable. Furthermore, for example, there was a problem that time and energy consumption required for formation of the thin films increased.
Moreover, when the time required for the formation of the thin films became long, there was a problem that productive efficiency of the thin films dropped and manufacturing cost rose.
Hence, the present invention aims at providing a thin film forming method and a thin film forming apparatus which can reduce degradation and dispersion of film qualities of thin films of respective surfaces of the substrate when depositing a material, which is made into particulates, on both sides of a substrate, for example, when forming thin films of oxide superconductors or the like.
In addition, the present invention aims at providing a thin film forming method and a thin film forming apparatus which can reduce production cost at the time of forming thin films, such as oxides superconductors, on both sides of a substrate.